what kind of method does gurobi use for solving LP? simplex??

[ingundinfo...@gmail.com]

Hi all,

I am very new in the field of LP and gurobi and I would like to know what kind of method gurobi uses for solving LP. Simplex method or maybe another existing method? Is there any resource available about it?

I am trying to write a small program to get familiar with gurobi. In order to get the number of iterations ( is this in simplex method? I guess so) and the number of solutions via Java, I write as follows:
            logger.info("Optimal value " + model.get(GRB.DoubleAttr.ObjVal)) ;
            logger.info("#iterations : " + model.get(GRB.DoubleAttr.IterCount ) ) ;
            logger.info("#solutions : "  +  model.get(GRB.IntAttr.SolCount) ) ;
And I receive the following as result :
#iterations : 0.0
#solutions : 1
I cannot understand why I am getting always 0 for #iterations and 1 for solutions. Is that normal? 

Is it the correct way to receive the number of iterations via model.get(GRB.DoubleAttr.IterCount )  ?

How can I understand ( is there a variable to check in java ) which LP method gurobi is using for my problem?

Thanks for your help!!
Regards

[Jakob Sch.]

Hi,

Unless you stated something else, gurobi will use the dual simplex method for solving linear problems. In order to change that you'll have to change the method parameter (see http://www.gurobi.com/documentation/5.6/reference-manual/method#parameter:Method). Maybe, if your model is very small, the presolving routines in gurobi were able to solve your problem so the simplex algorithm had not to be started.

Best regards,
Jakob

[ingundinfo...@gmail.com]

Hi Jakob,

Thank you very much for your reply! How may I use the parameter GRB.IntParam.Method in JAVA?  I would like to see which integer value it has chosen and applied for solving the LP problem.
And how can I set this parameter in Java?

Regards,
Ing.

[Jakob Sch.]

Hi,

The manual should help :) http://www.gurobi.com/documentation/5.6/reference-manual/java_details
In particular, you should take a look at http://www.gurobi.com/documentation/5.6/reference-manual/java_grbenv_set#javamethod:GRBEnv.set

Best regards,
Jakob

[ingundinfo...@gmail.com]

Thank you so much : )